The preschool the other person referred to, run by a Mrs. Vickery, is called Parkwood. There's no sign outside so you may not even spot it, so use the contact information in the other post. I've heard lots of parents rave about it so that's a good one to try. But preschools here are indeed good and popular, so you should apply at a couple in case of waiting lists and you definitely should visit several rather than setting your heart on one immediately. A friend just said yesterday that she had moved her son to Parkwood and he was very happy there.
My daughter went for three years to Holy Comforter (on Beulah Road, in the Episcopal church there) and we both were very pleased with it--they have a speech therapist who comes weekly to do lessons with all the kids, an art teacher, a music teacher, a science teacher who comes in, etc.
Another popular large preschool is Vienna Baptist, and I know several folks who happily send their kids to Faith Baptist Preschool on Center Street, which also has a kindergarten program. If you want a cooperative preschool (where parents are required to spend a certain amount of time working at the preschool--I believe there are professional teachers but parents must volunteer X amount of time for their kids to be in the preschool), there's F.B. Meekins Preschool located at a church right on Maple Street (Rt. 123) as you head towards Tysons Corner. Another well-regarded preschool is Wesley United Methodist off Moore Street; I know lots of parents whose kids have gone there and they were pleased.
Most important of all-- visit each one and spend some time there, even if you have to find babysitting for your child to do it. Getting the "vibe" of a place is vital and so is knowing your child. I visited one place that seemed too big and bustling but other parents loved it; I visited another (Holy Comforter) that seemed much calmer and it was great for us but other parents wanted a differet vibe for their bouncier little boys. So you may want to shop around for the "fit." Have fun and you really will find someplace great here! Remember, it's not college--if the place is focused on socialization and learning to get along with adults and other children, your daughter will be well prepared for kindergarten. Welcome to the DC area and take your daughter to lots of puppet shows, kids' plays and museums!